Document Notarius credential forwarding

docs/roadmap/implementation.md

@@ -1,6 +1,13 @@
 # Notarius Credential Forwarding Implementation Plan
 
-Status: In progress — 2026-09-16
+Status: Complete — 2026-09-16
+
+Release-ready summary: Narratio now accepts an optional typed
+`notarius.llm_api_key` environment reference, resolves it through the existing
+command bootstrap, forwards only that selected credential to Notarius, and
+redacts its value from captured subprocess streams. Existing configurations
+require no migration, and credential-only changes do not invalidate completed
+extraction work. Version selection and release publication remain separate.
 
 Implement the [feature roadmap](notarius-credential-forwarding.md) in the order
 below. Each stage is a bounded assignment for a gpt-5.6-terra coding agent.
@@ -237,7 +244,28 @@ Acceptance:
 
 ## Stage 4 — Document the operator contract and validate the whole feature
 
-Status: Not started
+Status: Complete — 2026-09-16
+
+Completion: Updated the canonical configuration, CLI, Notarius integration,
+internal configuration/adapter/extract, troubleshooting, and example guidance.
+The maintained annotated pipeline demonstrates the optional reference with a
+synthetic-value test fixture, and published release notes remain unchanged.
+The full repository validation and all three maintained asset builds succeeded;
+the macOS arm64 result is cross-compilation evidence only.
+
+Checks:
+
+- `GOWORK=off go mod tidy -diff` — pass with no changes.
+- `GOWORK=off go mod verify` — pass.
+- `GOWORK=off go test -count=1 ./...` — pass.
+- `GOWORK=off go test -race -count=1 ./...` — pass.
+- `GOWORK=off go vet ./...` — pass.
+- `GOWORK=off go build ./...` — pass.
+- `GOWORK=off go test ./internal/doccheck` — pass.
+- `GOWORK=off go test ./internal/config -run '^TestExamplesLoadAndValidate$'` — pass.
+- `git diff --check` and `gofmt -l` on changed Go files — pass.
+- `scripts/build-release-assets.sh v0.0.0-test <empty-mktemp-dir>` — pass for
+  Linux amd64, Linux arm64, and macOS arm64 cross-compilation.
 
 Read: `docs/config.md`, `docs/cli.md`, `docs/integrations/notarius.md`,
 `docs/internal/configuration.md`, `docs/internal/adapters.md`,